1. Field of the Invention
The present invention relates to an image signal processing apparatus for processing an image signal output from an image pickup device or photoelectric transducer and representative of a desired scene and outputting a corresponding still picture signal. More particularly, the present invention relates to an image signal processing device advantageously applicable to a digital camera or similar image pickup equipment capable of outputting a moving picture made up of a plurality of frames.
2. Description of the Background Art
A digital camera is a recent achievement in the imaging art and capable of picking up a desired scene with an image pickup device implemented by a CCD (Charge Coupled Device) image sensor, processing the resulting image signal, and recording the processed image signal in a memory card, magnetic disk, magnetic tape or similar data recording medium. A digital still camera, for example, digitizes an image signal representative of a single picture and output from a bidimensional color image pickup device. The resulting color image data are encoded by compression based on a JPEG (Joint Photographic Expert Group) or similar still picture compression coding system and then written to a data recording medium.
More specifically, the digital camera processes a plurality of frames of image signals continuously output from the image pickup device and delivers resulting image data to a monitor implemented by a color LCD (Liquid Crystal Display) panel. This allows the operator of the camera to perform framing and focusing before recording a still picture while watching a picture appearing on the monitor, i.e., an electronic finder. In parallel with the spread of the digital camera, there is an increasing demand for pictures of higher quality. For higher picture quality, the camera has recently been loaded with a color image pickup device having more than 1,300,000 pixels in its photosensitive array. With such a high pixel density image pickup device, pictures comparable in definition with pictures available with a silver halide photosensitive type of film can be achieved.
Japanese patent laid-open publication No. 108116/1998, for example, discloses a digital still camera capable of processing an image signal with software and storing the resulting image data in a semiconductor memory.
However, the problem with the processing of an image signal representative of a high definition image with a high pixel density, image pickup device is that an increase in the number of pixels to be dealt with results in an increase in processing time and processing load. While Japanese patent laid-open publication No. 22379/1997 teaches a general processor implemented as a microcomputer, the general processor does not give consideration to functions or conditions necessary for constructing a camera. When digital signal processing units are constructed into a single chip, the microcomputer taught in the above document is directed toward rapid signal processing between the signal processing units.
However, when it comes to a digital camera, processing an image signal representative of a single picture, encoding it by compression and recording the resulting image data in a data recording medium increases the processing time with an increase in the pixel density of the image pickup device. Further, when an image signal is continuously processed in order to continuously display an image being picked up, i.e., to implement a finder function, the processing load increases with an increase in the number of pixels and causes the individual frame of the image being displayed to be delayed from the actual scene. The delay or time lag sequentially increases and renders the finder function insufficient. In addition, the increase in processing load makes it difficult to execute other necessary processing and thereby slows down the operation of the overall image pickup equipment. To simply enhance the high-speed processing of a camera, use may be made of a large scale, image signal processing circuit and a processor operable at a higher speed. This, however, would increase the cost of the camera and would render the camera too bulky to carry. Moreover, power consumption would be aggravated to limit the drive time available with a secondary battery or similar battery. For these reasons, it has been difficult to realize a digital camera easy to use, simple in construction, and operable at a high speed.
It is therefore an object of the present invention to provide an image signal processing apparatus capable of adequately processing both a still picture and moving pictures and outputting the processed pictures.
In accordance with the present invention, an image signal processing apparatus for processing an image signal output from an image pickup device includes an image signal processing device for processing the image signal and outputting the resulting image data to either one of a first and a second output. A first bus is connected to the first output for transferring the image data while a first storage is connected to the first bus for storing the image data. A recording device is connected to the first bus for processing the image data read out of the first storage in a format matching with a data recording medium and recording the resulting processed image data in the medium. A second bus is connected to the second output for transferring the image data output via the second output. A reproducing and outputting device is connected to the first bus and second bus for reproducing an image represented by the image data output via the second output and outputting the resulting reproduced image. A main controller is connected to the first bus for controlling the various sections of the apparatus and setting an operation mode. The image signal processing device includes an output selector for selectively outputting the image data to the first output or the second output. When moving picture data are to be output, the image signal processing device outputs the moving picture data to the second output, but does not output them to the first output. When the image data are to be recorded in the data recording medium, the image signal processing device outputs the image data to the first output. The reproducing and outputting device receives the image data on the first bus or the second bus in accordance with the operation mode, reproduces the image data, and outputs the reproduced image data to a monitor.